The joint letter came on the occasion of her appointment, and the formation of the new government.

"We welcome your government's ambitious reform agenda that, together with ever closer alignment in foreign policy and steady progress in the Belgrade-Pristina dialogue, would move Serbia forward on its European path," Tusk and Juncker wrote, according to the EU website.

"We reiterate the European Union's unequivocal support for the European perspective of the Western Balkans and reassure you of our readiness to support you on your integration path," the letter said, and added:

"We look forward to working closely with you and your government to maintain stability and enhance prosperity of your country, your region and Europe as a whole."